BR112019001321B1 - Process for the oxidative dehydrogenation of ethane to ethylene. - Google Patents

Abstract

These are processes and associated reaction systems for the oxidative dehydrogenation of ethane. In particular, a process is provided which comprises supplying a feed gas comprising ethane and oxygen to a multitubular fixed bed reactor, allowing the ethane and oxygen to react in the presence of an oxidative dehydrogenation catalyst to produce a reactor effluent which comprises ethylene; supplying a refrigerant to an upstream region of an inner shell space of the reactor in a flow pattern that is countercurrent to the flow of the feed gas; and removing the refrigerant from the upstream region and supplying at least a portion of the refrigerant removed from the upstream region to the downstream region in a flow pattern that is concurrent with the flow of the feed gas.

Description

FIELD OF THE INVENTION

[001] The present invention relates to a process for the oxidative dehydrogenation of ethane.

BACKGROUND

[002] The oxidative dehydrogenation of ethane is known to result in ethylene, in a process of oxidative dehydrogenation (oxydehydrogenation; ODH). Examples of ethane ODH processes are, for example, described in US7091377, WO2003064035, US20040147393, WO2010096909 and US20100256432. The oxidative dehydrogenation of ethane converts ethane to ethylene. In this process, ethane reacts with oxygen in the presence of an ODH catalyst to produce a product stream comprising predominantly ethylene, along with unreacted reactants (such as ethane and oxygen), and typically other gases and/or by-products (such as such as carbon monoxide, carbon dioxide, water).

[003] In general, the ethylene yield in an ODH process is reduced by the undesirable combustion reactions of ethane and ethylene, both of which are highly exothermic and generate carbon dioxide and/or carbon monoxide. As is often the case in such exothermic processes, it is important to control the reaction temperature within a certain range to maintain efficient and safe plant operation and also to prolong catalyst life and inhibit undesirable side reactions. It is known that a multitube fixed bed reactor can be used to conduct such exothermic reactions, with the reactor employing a plurality of tubes containing a fixed bed of catalyst particulates, and a shell in which the tubes are contained through which coolant flows. to facilitate the removal of the heat of reaction.

[004] Normally, it is desirable to maintain isothermal conditions on the coolant side of the reactor. This is normally achieved by using a boiling medium (e.g. water/steam, kerosene) as the refrigerant, where the low temperature inlet feed gas is preheated to reaction temperature at the expense of the refrigerant entering the housing at a higher temperature, or by circulating a refrigerant that is in countercurrent flow with the flow of reactants through the tubes at a sufficiently high circulation rate so as to rapidly remove heat. However, fixed bed reactors used in exothermic reactions may still have the propensity to develop one or more "hot spots" in various regions of the reactor.

[005] In an attempt to avoid the undesirable formation of so-called "hot spots" (a localized temperature peak) in the catalyst bed, a commonly proposed solution is to reduce the diameter of the tubes in order to increase the heat transfer rate by unit volume of the catalyst. However, this typically increases the cost associated with building the reactor and also increases the amount of time required to load and unload the catalyst into the tubes. Likewise, it can also somewhat limit the size/shape of the catalyst that can be used. Likewise, if tube lengths are significantly increased, the pressure drop across the reactor may also increase undesirably. Another commonly proposed solution is to operate with lower throughput or lower conversion, for example, diluting the catalyst with an inert substance. However, this also has the disadvantage of increasing cost and typically increases the difficulty of later recovery of spent reactor catalyst for regeneration, if desired.

[006] Therefore, the present inventors sought to provide improved processes for the oxidative dehydrogenation of ethane. In particular, the present inventors have sought to provide ODH processes that utilize a multitube fixed bed reactor in which the generation of hot spots in the catalyst bed is avoided or reduced, thereby preventing or minimizing the risk of a reactor leak.

SUMMARY

[007] In one aspect, there is provided a process for the oxidative dehydrogenation of ethane to ethylene, wherein the process comprises: providing a multitubular fixed bed reactor comprising a reactor inlet, an interior casing space, a perforated partition that divides the inner shell space into an upstream region and a downstream region, and a plurality of reactor tubes, wherein the plurality of reactor tubes comprise a catalyst bed comprising an oxidative dehydrogenation catalyst; supplying a feed gas comprising ethane and oxygen to the reactor inlet and allowing the ethane and oxygen to react in the presence of the oxidative dehydrogenation catalyst to produce a reactor effluent comprising ethylene; supplying a refrigerant to the upstream region in a flow pattern that is countercurrent to the flow of the feed gas through the plurality of reactor tubes; and withdrawing the refrigerant from the upstream region and supplying at least a portion of the refrigerant withdrawn from the upstream region to the downstream region in a flow pattern that is concurrent with the flow of the feed gas through the plurality of reactor tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

[008] Some specific exemplary embodiments of the disclosure may be understood by referring, in part, to the following description and accompanying drawings.

[009] Figure 1 is a schematic illustration showing an exemplary embodiment of the present disclosure.

[0010] While the present disclosure is susceptible to various modifications and alternative forms, specific exemplary embodiments have been shown in the Figures and are described herein in more detail. However, it is to be understood that the description of specific exemplary embodiments is not intended to limit the invention to the particular forms disclosed, but otherwise, the present disclosure should cover all modifications and equivalents as illustrated, in part, by the claims. attached.

DETAILED DESCRIPTION

[0011] The present invention makes use of the observation that in an ODH process using a multitubular fixed bed reactor, hot spots almost always occur in an upstream portion of the catalyst bed; therefore, a low coolant temperature would be better here. However, at such a low coolant temperature, there is plenty of room for an axial temperature rise along the length of the reactor without the risk of a hot spot formation in the downstream portion of the catalyst bed.

[0012] Consequently, the present inventors have disclosed that, using the processes disclosed herein, it is possible to minimize or prevent the formation of hot spots in an upstream portion of the catalyst bed, while simultaneously achieving relatively high productivity throughout the entire catalyst bed. , without the need to decrease the tube diameter and/or increase the tube length. In particular, it has been found that these advantages can be achieved by dividing the interior casing space of a multitubular fixed-bed reactor into an upstream region and a downstream region, and supplying coolant to the upstream and downstream regions in a pattern. flow rate, contrary to normal practice, the refrigerant side isothermy is deliberately impaired by the refrigerant circulating in the upstream region in the countercurrent flow with respect to the supply gas flow and circulating refrigerant in the downstream region in cocurrent flow with respect to the supply gas flow at what would normally be considered an insufficient flow rate.

[0013] In accordance with the methods of the present description, the refrigerant is supplied to an upstream region of an interior casing space of a multitubular fixed bed reactor in countercurrent flow with respect to the flow of feed gas through the plurality of reactor tubes. The temperature of the coolant in the upstream region will generally increase, due to the removal of heat of reaction generated in the upstream portion of the catalyst bed, such that the coolant will be hotter when withdrawn from the upstream region at an upstream coolant outlet. than supplied to the upstream region on an upstream refrigerant inlet.

[0014] The coolant taken from the upstream region is then supplied to a downstream region of the multitubular fixed bed reactor interior space in cocurrent flow to a downstream coolant inlet that is fluidly connected to the upstream coolant outlet through a refrigerant circuit. As in the upstream region, the temperature of the coolant in the downstream region will also generally increase, due to the removal of reaction heat generated in the downstream portion of the catalyst bed, so that the coolant is warmer when withdrawn from the downstream region in a downstream refrigerant outlet than when supplied to the downstream region at a downstream refrigerant inlet.

[0015] In general, the coolant is supplied to the upstream and downstream regions of the reactor's inner casing space at a flow rate that is low enough to allow a rise in the temperature of the coolant as it flows through the respective upstream regions. upstream and downstream of the reactor's inner casing space. For example, refrigerant can be supplied to the upstream region at a flow rate sufficient to allow a temperature rise of the refrigerant of about 1 to 25 °C, or 5 to 20 °C, or 5 to 15 °C in the upstream region, as measured from an upstream refrigerant inlet positioned at or near the bottom of the upstream region to an upstream refrigerant outlet positioned at or near the top of the upstream region.

[0016] Likewise, refrigerant can be supplied to the downstream region at a flow rate sufficient to allow a temperature rise of the refrigerant of about 1 to 30 °C, or 5 to 25 °C, or 5 to 20 °C in the downstream region, as measured from a downstream refrigerant inlet positioned at or near the top of the downstream region to a downstream refrigerant outlet positioned at or near the bottom of the downstream region . As such, the reactor is operated in a manner where refrigerant-side isothermicity is deliberately compromised by using countercurrent flow in the upstream region and co-current refrigerant flow in the downstream region, at what would generally be considered a flow rate. very low, which thus allows the process side to become remarkably isothermal.

[0017] In accordance with the oxidative dehydrogenation processes of the present disclosure, a feed gas comprising ethane and oxygen is supplied to the inlet of a multitubular fixed bed reactor. As used herein, the term "feed gas" is understood to refer to the entire gas stream(s) at the reactor inlet(s). Thus, as one skilled in the art will appreciate, the feed gas is often a combination of one or more gas streams, such as an ethane stream, an oxygen-containing stream, a recycle gas stream, etc. Optionally, in addition to ethane and oxygen, the feed gas may also comprise other alkanes (e.g. methane, propane), carbon monoxide, carbon dioxide, hydrogen, steam, an inert gas (e.g. nitrogen, helium and/or argon) and/or various by-products of the ODH reaction (eg acetylene, acetic acid).

[0018] Ethane and oxygen can be added to the reactor as a mixed feed, optionally comprising other components in them, at the same reactor inlet. Alternatively, ethane and oxygen can be added in separate feeds, optionally comprising other components therein, to the reactor at the same reactor inlet or at separate reactor inlets. Furthermore, the order and manner in which the feed gas components are supplied to the reactor inlet are not particularly limited and therefore the components can be combined simultaneously or sequentially. In addition, the feed gas components may optionally be vaporized, preheated and mixed (if desired) before being supplied to the reactor inlet using means known to those skilled in the art. For example, preheating techniques may include, for example, heat exchange from steam, a heat transfer fluid (e.g. coolant), reactor effluent, and/or an oven.

[0019] The ethane in the feed gas can be from any suitable source, including natural gas, as long as the impurities are sufficiently removed and may include fresh ethane, a recycle of unreacted ethane from the reactor effluent, or a combination thereof . Likewise, oxygen can originate from any suitable source, such as air or a stream of high-purity oxygen. Such high purity oxygen may be greater than 90%, preferably greater than 95%, more preferably greater than 99%, and most preferably greater than 99.4% pure.

[0020] In general, the molar ratio of molecular oxygen to ethane in the feed gas at the entrance to the reactor can be in the range of 0.01 to 1, more appropriately 0.05 to 0.5. Preferably, the feed gas comprises from 5 to 35% by volume of oxygen, in relation to the total volume of the feed gas, more suitably 20 to 30% by volume of oxygen and 40 to 80% by volume of ethane, more suitably 50 to 70% by volume of ethane and less than 80% (0 to 80)% by volume of an inert gas, more suitably less than 50% (0 to 50)% by volume of an inert gas, more suitably 5 to 35% by volume of an inert gas, more appropriately 10 to 20% by volume of an inert gas. Generally speaking, the concentration of oxygen in the feed gas should be less than the concentration of oxygen that would form a flammable mixture at the reactor inlet or outlet under prevailing operating conditions.

[0021] Multitube fixed bed reactors suitable for use in the present disclosure are not particularly limited and may include any of a variety known in the art. Providing a multi-tube fixed bed reactor comprising a reactor inlet, an inner casing space, a perforated partition dividing the inner casing space into an upstream region and a downstream region, and a plurality of reactor tubes, in that the plurality of reactor tubes comprises a catalyst bed comprising an oxidative dehydrogenation catalyst. Optionally, in addition to the catalyst bed, the reactor tubes may further comprise a bed of an inert material.

[0022] Inside the reactor, the upper ends of the reactor tubes are typically held in place by an upper tube plate and are in fluid communication with the reactor inlet. Likewise, the lower ends of the reactor tubes are typically held in place by a lower tube plate and are in fluid communication with the reactor outlet. Preferably, the reactor tubes are arranged substantially vertically within the reactor, so that they are no more than 5° from the vertical, and the upper and lower tube plates are positioned within the reactor at a distance. substantially horizontally, such that they are no more than 3° from the horizontal.

[0023] While the size and number of reactor tubes within a multitube fixed bed reactor can vary widely from reactor to reactor, a reactor tube used in a commercial reactor can generally have a length of 1 to 25 meters and a diameter inner tube from 10 to 80 millimeters. Also, the number of reactor tubes can vary and can vary by thousands, for example up to 50,000.

[0024] A perforated partition that extends transversely to the plurality of reactor tubes divides the reactor interior casing space into an upstream region and a downstream region. In general, the perforated partition is a plate with a plurality of holes through which the reactor tubes can pass. A perforated partition can be of any suitable material, such as metal (eg carbon steel).

[0025] The perforated division is typically arranged such that the upstream region is at least 10% of the length of the reactor tube, or at least 15%, or at least 20%, or at least 25% in it. base and a maximum of 70% of the length of the reactor tube, or a maximum of 40%, or a maximum of 30%, or a maximum of 25%, or a maximum of 20%, or a maximum of 15%, on the same basis, or of 10 % to 30% of the reactor tube length, or from 10% to 25%, or from 10% to 20%, or from 10% to 15%, or from 15% to 30%, or from 15% to 25% , or from 15% to 20%, on the same basis. Correspondingly, the downstream region is typically at least 30% of the reactor tube length, or at least 60%, or at least 70%, or at least 75%, or at least 80%, or at least 85%, in the same base, and maximum 90% of the reactor tube length, or maximum 85%, or maximum 80%, or maximum 75%, on the same base, or from 70% to 90%, or from 75% to 90%, or 80% to 90%, or 70% to 85%, or 75% to 85%, or 80% to 85%, one on the same basis. Advantageously, by dividing the space of the inner casing into two separate regions, it is possible to improve the distribution of the coolant in the reactor, thus providing more control over the temperature.

[0026] In accordance with the ODH processes of the present disclosure, ethane and oxygen are allowed to react in the presence of an oxidative dehydrogenation catalyst to produce a reactor effluent comprising ethylene. In general, various ODH processes are known and described in the art and the ODH processes of the present disclosure are not limited in that regard. Thus, one skilled in the art can conveniently utilize any of these processes in accordance with the ODH processes of the present disclosure. For example, suitable ODH processes, including catalysts and other process conditions, include those described in US7091377, WO2003064035, US20040147393, WO2010096909 and US20100256432 mentioned above, which are incorporated herein by reference.

[0027] Suitably, the temperature in the plurality of reactor tubes is in the range of 100 to 600 °C, preferably in the range of 200 to 500 °C. Furthermore, the pressure in the plurality of reactor tubes is in the range of 0.1 to 3 Mpaa (i.e. absolute MPa”) (1 to 30 bara, i.e. “absolute bar”), or from 0.1 to 2 Mpaa (1 to 20 bara), or from 0.1 to 1.5 Mpaa (1 to 15 bara), or from 0.2 to 1.0 MPaa (2 to 10 bara), or from 0.3 to 1 .0 Mpaa (3 to 10 bara).

[0028] Suitable oxidative dehydrogenation catalysts for use in the present disclosure are not particularly limited and may include any ethane oxidative dehydrogenation catalyst. The amount of this catalyst is not essential. Preferably, a catalytically effective amount of the catalyst is used, i.e., an amount sufficient to promote the ethane oxydehydrogenation reaction.

[0029] Examples of suitable oxidative dehydrogenation catalysts include, but are not necessarily limited to, one or more mixed metal oxide catalysts comprising molybdenum, vanadium, niobium and optionally tellurium as the metals and may have the following formula: Mo1VaTebNbcOn wherein: a, b, c and n represent the ratio between the molar amount of the element in question and the molar amount of molybdenum (Mo); a (for V) is 0.01 to 1, preferably 0.05 to 0.60, more preferably 0.10 to 0.40, more preferably 0.20 to 0.35, most preferably 0.25 to 0.30; b (for Te) is 0 or from > 0 to 1, preferably 0.01 to 0.40, more preferably 0.05 to 0.30, more preferably 0.05 to 0.20, most preferably 0.09 to 0 .15; c (for Nb) is >0 to 1, preferably 0.01 to 0.40, more preferably 0.05 to 0.30, more preferably 0.10 to 0.25, most preferably 0.14 to 0.20 ; and n (for O) is a number that is determined by the valence and frequency of elements other than oxygen.

[0030] Optionally, a catalyst bed may comprise more than one oxidative dehydrogenation catalyst. For example, in one embodiment, a catalyst bed may comprise a plurality of oxidative dehydrogenation catalysts having varying activity levels (e.g., so as to vary the activity level along the length of the reactor tube). Furthermore, if desired, the catalyst bed may further comprise inert material (e.g. to dilute and/or reduce the activity of the catalyst bed). Optionally, in another embodiment, a catalyst bed may comprise an oxidative dehydrogenation catalyst comprising tellurium in an upstream catalyst bed positioned within the upstream region and an oxidative dehydrogenation/oxygen removal catalyst in a positioned downstream catalyst bed. within the downstream region.

[0031] Preferably, the oxidative dehydrogenation catalyst is heterogeneous and in particulate form. Furthermore, preferably said heterogeneous catalyst is porous, specifically a porous particulate catalyst.

[0032] As mentioned, according to the processes of the present description, the refrigerant is supplied to an upstream region of the interior casing space of a multitubular fixed bed reactor in a flow pattern that is countercurrent with the flow of the flue gas. feeding through the plurality of reactor tubes. Refrigerant is typically supplied to the upstream region through an upstream refrigerant inlet located at or near the bottom of the upstream region. Likewise, refrigerant is typically removed from the upstream region through an upstream refrigerant outlet located at or near the top of the upstream region.

[0033] Refrigerant may be supplied to and removed from the upstream region of the reactor interior casing space in any suitable manner, provided that the flow of refrigerant in the upstream region is countercurrent to the flow of feed gas through the plurality of reactor tubes. Typically, the refrigerant is supplied to the upstream region through a refrigerant circuit, which optionally comprises one or more cooling apparatus (e.g. heat exchanger, steam drum, etc.) and one or more circulation pumps. .

[0034] Further, in accordance with the processes of the present disclosure, the refrigerant is supplied to the region downstream of the interior casing space of the multitubular fixed bed reactor in a flow pattern that is concurrent with the flow of the feed gas through the plurality of reactor tubes. Refrigerant is supplied to the downstream region through a downstream refrigerant inlet that is fluidly connected to the upstream refrigerant outlet and is typically located at or near the top of the downstream region. Refrigerant is removed from the downstream region through a downstream refrigerant outlet located at or near the bottom of the downstream region. Refrigerant may be supplied to and removed from the downstream region of the interior space of the reactor shell in any suitable manner, provided that the flow of refrigerant in the downstream region is co-current with the flow of feed gas through the plurality of reactor tubes. Typically, the refrigerant is supplied from the upstream region to the downstream region via a refrigeration circuit, which optionally comprises a cooling apparatus (e.g. heat exchanger, steam drum, etc.) and a circulation pump.

[0035] The coolant is preferably supplied to the upstream region of the reactor's inner casing space at a flow rate sufficient to allow a coolant temperature rise of about 1 to 25°C, or 5 to 20° C, or 5 to 15 °C, as measured from an upstream refrigerant inlet positioned at or near the bottom of the upstream region to an upstream water outlet positioned at or near the top of the upstream region .

[0036] Likewise, the refrigerant is preferably supplied to the downstream region at a flow rate sufficient to allow a temperature rise of the refrigerant of about 1 to 30 °C, or 5 to 25 °C, or 5 to 20 °C, as measured from a downstream refrigerant inlet positioned at or near the top of the downstream region to a downstream refrigerant outlet positioned at or near the bottom of the downstream region.

[0037] As will be appreciated by one skilled in the art, suitable upstream and downstream refrigerant flow rates can vary widely depending, at least in part, on the specific configuration of the multitubular fixed bed reactor (e.g., the length and the inner diameter of the tubes inside the reactor, the comparative size of the upstream and downstream regions), the process conditions, the activity level of the ODH catalyst used, the size and/or shape of the catalyst used, as well as the particular heat capacity of the refrigerant. It is within the skill of one skilled in the art to select suitable upstream and downstream refrigerant flow rates, taking into account, for example, the aforementioned parameters. Accordingly, if desired, simulation models can be used to determine the appropriate refrigerant flow rates necessary to achieve the desired refrigerant temperature differentials. Reference is made to, for example, A. Soria Lopez, et al., “Parametric Sensitivity of a Fixed Bed Catalytic Reactor”, Chemical Engineering Science, Volume 36 (1981), pages 285 to 291, for further discussion concerning the effects of temperature variation in a concurrent refrigerant in the operation of a fixed bed reactor. Suitable refrigerant may be any fluid suitable for heat transfer, for example a molten salt or an organic material suitable for heat exchange (e.g. oil, kerosene, etc.). Preferably, the cooling in the present process is carried out under non-boiling conditions. In particular, it is preferred that in the present process the refrigerant does not boil.

[0038] Suitably, the upstream inlet refrigerant temperature is typically at least 250°C, or at least 275°C, or at least 300°C, or at least 310°C, or at least 320°C and typically at most 499 °C, or at most 450 °C, or at most 425 °C, or at most 400 °C, or at most 380 °C, or from 250 °C to 499 °C, or from 250 °C to 400 °C, or from 300 °C to 400 °C, or from 320 °C to 380 °C.

[0039] Furthermore, in accordance with the methods of the present disclosure, the coolant is preferably supplied to the downstream region of the reactor's inner casing space via the downstream coolant inlet at a downstream inlet coolant temperature (i.e. , the temperature of the refrigerant measured at the inlet of the downstream refrigerant) that exceeds that of the temperature of the inlet refrigerant upstream (that is, the temperature of the refrigerant as measured at the inlet of the upstream refrigerant) by at least 1 °C, or at least 3 °C above, or at least 5 °C above, or at least 10 °C above, and typically at most 25 °C above, or at most 20 °C above, or at most 15 °C, or from 1 °C to 25 °C above, or from 5 °C to 25 °C above, or from 5 °C to 20 °C above, or from 5 °C to 15 °C above.

[0040] Suitably, the downstream inlet refrigerant temperature is typically at least 251 °C, or at least 255 °C, or at least 260 °C, or at least 275 °C, or at least 285 °C, or at least 300 °C, or at least 310 °C, or at least 320 °C, and typically at most 500 °C, or at most 450 °C, or at most 425 °C, or at most 400 °C, or maximum 380 °C, or 251 °C to 500 °C, or 255 °C to 500 °C, or 260 °C to 500 °C, or 251 °C to 400 °C, or 300 ° C to 400 °C, or from 320 °C to 380 °C.

[0041] Optionally, the heat that is removed from the reactor can be used to heat the feed gas and/or refrigerant that is supplied to the reactor. In addition, if desired, the heat removed can also be used to generate steam (or preheat boiler feedwater) for use as an energy source, including as steam or transformed into energy.

[0042] In another embodiment of the present invention, the refrigerant drawn from the upstream region is divided into at least two portions, and one of the at least two separate refrigerant portions is supplied to the downstream region in a flow pattern that is concurrent with the flow of feed gas through the plurality of reactor tubes. In said embodiment, the relative amount of the divided portion of refrigerant that is supplied to the downstream region, based on the total amount of refrigerant withdrawn from the upstream region, is suitably 30 to 70% by volume, more suitably 40 to 60 % by volume, more appropriately 45 to 55% by volume.

[0043] Reference is now made to Figure 1, which is a schematic view of a reaction system for the oxidative dehydrogenation of ethane, in accordance with certain embodiments of the present disclosure. It will be clear to the person skilled in the art that as a schematic diagram this figure does not show all necessary inputs, outputs, recycling streams, etc., which may be present in the reaction system. Furthermore, in the figure, as will be appreciated, elements may be added, exchanged and/or deleted in order to provide any number of additional embodiments. Furthermore, as will be seen, the proportion and relative scale of the elements given in the Figure are intended to illustrate the embodiments of the present disclosure and should not be interpreted in a limiting sense.

[0044] It should further be appreciated that the orientation/configuration shown in Figure 1 is not intended to be limiting or exhaustive of all possible orientations/configurations, but is intended to be only an example provided to illustrate the spirit of the invention. For example, the reactor inlet is illustrated as being positioned at the top of the reactor with the flow of reactants descending to the reactor outlet positioned at the bottom; however, it should be understood that the orientation may vary from that shown in Figure 1. For example, the reactor orientation may be reversed from that shown in Figure 1 such that the reactor inlet is positioned, for example, at the bottom of the reactor with the flow of reactants heading towards an outlet positioned at the top of the reactor.

[0045] The multitubular fixed bed reactor (1) comprises the reactor inlet (2), the reactor shell (3), the perforated partition (4) and a plurality of open reactor tubes (5) positioned substantially parallel to the central longitudinal geometric axis (6) of the reactor (1). The upper ends (7) of the reactor tubes (5) are connected to a substantially horizontal upper tube plate (8) and the lower ends (9) of the reactor tubes (5) are connected to a substantially horizontal lower tube plate. (10). The upper tube plate (8) and the lower tube plate (10) are supported by the inner wall of the reactor (1).

[0046] The reactor tubes (5) contain a catalyst bed (11) comprising an oxidative dehydrogenation catalyst (12). In addition to the catalyst bed (11), the reactor tubes (5) may optionally further comprise a bed of inert material, such as an inert bed (13). Typically, the catalyst bed (11) is supported in the reactor tubes (5) by catalyst support means (not shown) disposed at the lower ends (9) of the reactor tubes (5).

[0047] The perforated partition (4) is a plate with a plurality of openings through which the reactor tubes (5) can pass. The perforated partition (4) divides the interior space of the housing (14) into the upstream region (15) and the downstream region (16).

[0048] According to the processes of the present description, a feed gas (17) comprising ethane and oxygen is supplied to the reactor (1) through one or more inlets, such as the inlet of the reactor (2) which is in fluid communication with the upper ends (7) of the reactor tubes (5). In the reactor tubes (5), the feed gas (17) comes into contact with the catalyst bed (11). Contacting the feed gas in the presence of oxidative dehydrogenation catalyst (12) under appropriate reaction conditions as described above converts at least a portion of the ethane to ethylene, water and reaction by-products, if any. Reactor effluent (18) exits the reactor (1) through one or more outlets, such as the reactor outlet (19), which is in fluid communication with the lower ends (9) of the reactor tubes (5).

[0049] As shown in Figure 1, refrigerant is supplied to the upstream region (15) through the upstream refrigerant inlet (20) and is removed from the upstream region (15) through the upstream refrigerant outlet (21) ). Furthermore, the refrigerant is supplied to the downstream region (16) through the downstream refrigerant inlet (22), which is connected to the upstream refrigerant outlet (21) through the refrigeration circuit (23) and is removed from the downstream region (16) through the upstream refrigerant outlet (24). In both the upstream and downstream regions, the circulating refrigerant will absorb heat by contacting the reactor tubes (5) such that the refrigerant will generally be hotter when withdrawn from the upstream or downstream refrigerant outlet than when it is removed. supplied to the respective upstream or downstream refrigerant inlets. Suitably, a refrigeration apparatus (not shown) may optionally be used to remove heat from the refrigerant before it is supplied to the upstream and/or downstream regions. Optionally, the internal space of the housing (14) can be provided with baffles (not shown) to guide the coolant.

[0050] As mentioned earlier, refrigerant is supplied to the upstream region (15) in a flow pattern that is countercurrent with the flow of feed gas through the reactor tubes (5) and is supplied to the downstream region (16). ) in a flow pattern that is concurrent with the flow of the feed gas through the reactor tubes (5). Refrigerant is preferably supplied to the upstream region (15) at a flow rate such that the upstream outlet refrigerant temperature, as measured at the upstream refrigerant outlet (21), exceeds the upstream inlet refrigerant temperature. , as measured at the upstream refrigerant inlet (20), at 1 to 25 °C. The refrigerant is preferably supplied to the downstream region (16) at a flow rate such that the downstream refrigerant outlet temperature measured at the downstream refrigerant outlet (24) exceeds the downstream inlet temperature measured at the refrigerant inlet. downstream (22) at 1 to 30°C.

[0051] The present invention is also applicable to a process for the oxidative dehydrogenation of alkanes having a carbon number greater than ethane, in particular alkanes having a carbon number of 3 to 6 carbon atoms, including propane, butane, pentane and hexane. , more specifically propane and butane, more specifically propane.

[0052] The invention is further illustrated by the Examples below.

EXAMPLES

[0053] In the present Examples, a process for the oxidative dehydrogenation (ODH) of ethane to ethylene is carried out in a multitubular fixed bed reactor comprising a reactor inlet, an interior casing space, a perforated partition dividing the inner casing in an upstream region and a downstream region, except for (reference) Example 1 (where no such partition is used), and a plurality of reactor tubes, wherein the reactor tubes comprise a catalyst bed comprising an oxidative dehydrogenation catalyst. The length of each tube is 6 meters. The inside diameter of each tube is 1.91 cm (0.75 inch).

[0054] A feed gas comprising ethane and oxygen is supplied to the reactor inlet. The temperature of the feed gas at said inlet is 160°C. Ethane and oxygen are allowed to react in the presence of the aforementioned catalyst to produce a reactor effluent comprising ethylene. In addition, a molten salt refrigerant is supplied to the upstream region in a flow pattern that is countercurrent with the flow of the feed gas through the reactor tubes, the refrigerant is withdrawn from the upstream region and the refrigerant withdrawn from the region. upstream is supplied to the downstream region in a flow pattern that is concurrent with the flow of feed gas through the reactor tubes. A configuration to run Examples 2, 3, and 4 is shown in Figure 1.

[0055] In the upstream part of the reactor, the temperature of the process stream comprising reactants and/or products (hereinafter referred to as "process temperature") increases as a consequence of the exothermic ethane ODH reaction occurs. Said process temperature is equal to the catalyst temperature. When moving along the length of the reactor from the upstream reactor inlet, said process temperature increases to a certain maximum temperature (peak), after which the process temperature would decrease due to the fact that the ethane concentration decrease resulting in less heat production. A relatively high peak temperature for the process stream, compared to the average temperature of the process stream, is disadvantageous as it increases the risk of a reactor leak.

[0056] In the present Examples, the effect of the aforementioned perforated partition, and its position along the length of the reactor, on the difference between the peak process temperature and the mean process temperature is evaluated. Generally, the greater the last temperature difference, the greater the likelihood of a reactor leak. Temperature data (in °C) and perforated partition positions (distance in meters) from the upstream upper side, in relation to a variety of cases, are shown in Table 1 below. For Examples 2, 3 and 4, respectively, the upstream region is 63%, 37%, and 25%, respectively, of the length of the reactor tubes.

[0057] For Examples 2 to 4, the temperature data (in °C) in Table 1 also includes: 1) the difference between the outlet refrigerant temperature and the inlet refrigerant temperature in the upstream region (3rd column from Table 1); 2) the difference between the outlet refrigerant temperature and the inlet refrigerant temperature in the downstream region (4th column of Table 1); and 3) the difference between the inlet refrigerant temperature in the downstream region and the inlet refrigerant temperature in the upstream region (5th column of Table 1).

[0058] In Example 1 (reference), no perforated partitions are used (i.e., no separate upstream and downstream regions), and refrigerant is supplied to the entire internal space of the enclosure in a flow pattern that is countercurrent with the flow of feed gas through reactor tubes where refrigerant is supplied to an inlet at the bottom and withdrawn at an outlet at the top. In said Example 1, the difference between the outlet refrigerant temperature (355°C) and the inlet refrigerant temperature (350°C) is 5°C. In all Examples 2 to 4, the difference between the downstream outlet refrigerant temperature (355 °C) and the upstream inlet refrigerant temperature (350 °C) is also 5 °C.

[0059] Furthermore, in the present Examples, the space-time-yield (STY) is set at 700 g of ethylene per liter of catalyst per hour. In addition, the ethane conversion is set at 55% and the ethylene selectivity at 87%. Said ethane and STY conversion is kept constant at said levels by adjusting catalyst activity. The total and partial pressures of ethane (C2H6) and oxygen (O2) at the upstream reactor inlet are kept constant: Ptotal = 0.6 MPa (6 bar); pC2H6 = 0.42 MPa (4.2 bar); pO2 = 0.18 MPa (1.8 bar). The hourly space velocity of the gas (GHSV) is 1950 h-1. The refrigerant flow rate is kept constant at 1000 kg/hour/tube.TABLE 1

[0060] Surprisingly, it follows from the results of Table 1 above that by providing a perforated partition in the reactor (thus creating an upstream region and a downstream region) and having a countercurrent refrigerant flow in the upstream region and a refrigerant flow in cocurrent in the downstream region, the difference between the peak process temperature and the average process temperature can advantageously be kept relatively small, thus avoiding or minimizing the aforementioned risk of a reactor leak. The difference between the peak process temperature and the average process temperature is advantageously only 12.8 °C (Example 2), 9.1 °C (Example 3) and 7.2 °C (Example 4), as opposed to at 17.9°C in Example 1 (reference) where no perforated partition is used.

Claims (8)

1. Process for the oxidative dehydrogenation of ethane to ethylene, characterized in that it comprises: providing a multitubular fixed bed reactor (1) comprising a reactor inlet (2), an inner casing space (14), a partition perforated (4) that divides the inner shell space (14) into an upstream region (15) and a downstream region (16), and a plurality of reactor tubes (5), wherein the plurality of reactor tubes (5) comprises a catalyst bed comprising an oxidative dehydrogenation catalyst; supplying a feed gas comprising ethane and oxygen to the reactor inlet (2) and allowing the ethane and oxygen to react in the presence of the oxidative dehydrogenation catalyst to produce a reactor effluent comprising ethylene; supplying a refrigerant to the upstream region (15) in a flow pattern that is countercurrent to the flow of the feed gas through the plurality of reactor tubes (5); and, withdrawing the refrigerant from the upstream region (15) and supplying at least a portion of the refrigerant withdrawn from the upstream region (15) to the downstream region (16) in a flow pattern that is concurrent with the flow of the exhaust gas. feeding through the plurality of reactor tubes (5); and, wherein the refrigerant is supplied to the downstream region (16) at a downstream refrigerant inlet (22) at a downstream inlet refrigerant temperature, and is removed from the downstream region (16) at a refrigerant outlet. downstream (24) at a downstream outlet refrigerant temperature, and wherein the downstream outlet refrigerant temperature exceeds the downstream inlet refrigerant temperature by 1 to 30°C. 2. Process according to claim 1, characterized in that the refrigerant is supplied to the upstream region (15) at an upstream refrigerant inlet (20) at an upstream refrigerant inlet temperature of 250 °C at 499°C. 3. Process according to claim 1, characterized in that the refrigerant is supplied to the upstream region (15) at an upstream refrigerant inlet (20) at an upstream refrigerant inlet temperature of 250 °C at 400°C. 4. Process according to claim 1, characterized in that the refrigerant is supplied to the downstream region (16) at a downstream refrigerant inlet (22) at a downstream inlet refrigerant temperature of 251 °C at 500°C. Process according to any one of claims 1 to 4, characterized in that the refrigerant is supplied to the upstream region (15) at an upstream refrigerant inlet (20) at an upstream inlet refrigerant temperature, and is removed from the upstream region (15) at an upstream refrigerant outlet (21) at an upstream outlet refrigerant temperature, and wherein the upstream outlet refrigerant temperature exceeds the upstream inlet refrigerant temperature at 1°C to 25°C. Process according to any one of claims 1 to 5, characterized in that the refrigerant is supplied to the upstream region (15) at an upstream refrigerant inlet (20) at an upstream inlet refrigerant temperature, and is supplied to the downstream region (16) at a downstream refrigerant inlet (22) at a downstream inlet refrigerant temperature, and wherein the downstream inlet refrigerant temperature exceeds the upstream inlet refrigerant temperature at 1 to 25°C. 7. Process according to any one of claims 1 to 6, characterized in that the upstream region (15) is from 10 to 30% of the length of the reactor tubes (5). 8. Process according to any one of claims 1 to 7, characterized in that the oxidative dehydrogenation catalyst in the catalyst bed has the following formula: Mo1VaTebNbcOn in which: a, b, c and n represent the ratio between the molar amount of the element in question and the molar amount of molybdenum; a is from 0.01 to 1; b is 0 or from > 0 to 1; c is > 0 to 1; and n is a number that is determined by the valence and frequency of elements other than oxygen.

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